1. Field of the Invention
The present invention relates, in general, to an apparatus and method for converting interlaced field image data into progressive image data in image processing techniques and, more particularly, to an apparatus and method for performing intra-field interpolation for a de-interlacer, which calculates a direction in which pixel values are changed using the variations and correlations between the pixel values of the regions on two lines in one field, and outputs an interpolated value depending on the direction, thus enabling a field to be interpolated in the change direction.
2. Description of the Related Art
An interlace mode denotes a mode of displaying only a half of horizontal lines in a single image frame when a single image is displayed in a cathode ray tube television used in normal homes (regardless of National Television System Committee (NTSC) mode (US and Korea) or Phase Alternation by Line system (PAL) mode (Europe)). That is, interlaced image data are implemented with two fields by dividing one frame into an odd field and an even field, as shown in FIG. 1.
For example, in case of a 480 line NTSC mode (exactly, 487 active lines of 525 lines), one frame is divided into two fields each consisting of 240 lines and displayed thereby. The fields each having 240 lines, divided in this way, are alternately displayed on a screen every 1/60 second (480/60i). In this mode, there is a problem in that horizontal lines can be easily, visually discerned when the size of a display screen exceeds about 30 inches. Therefore, in the interlace mode, it can be considered that about 30 frames for one second are displayed.
In the meantime, a progressive (scan) mode is the term first defined to describe various aspects of a Digital Versatile Disc (DVD) player, and an image reproduction scheme, such as the progressive scan, can be easily understood by referring to the monitor of a computer. Currently, the progressive scan mode denotes a mode in which a computer monitor, a digital TV, such as a Plasma Display Panel (PDP) or Liquid Crystal Display (LCD) TV, or a Digital Satellite System (DSS) displays video in frames, that is, the entire image of each frame at one time, like the case where a film is projected onto a screen.
For example, the progressive scan mode allows a 480 line image to be displayed at one time every 1/60 second in the form of a full frame image (480/60p). Consequently, in the progressive scan mode, 60 frames per second are fully implemented. Therefore, the progressive scan mode enables an image quality far higher than that of the interlace mode to be realized, and does not cause a screen blur, such as aliasing at the edge of a moving object (motion artifact).
As described above, image data are processed and displayed on a screen in the progressive scan mode used in a computer monitor or etc., without being processed in the interlace mode, depending on display devices. At this time, in order to normally process interlaced image signals in a display device that processes progressive image data, a separate system for converting the interlaced image signals into progressive image signals should be provided in the display device.
In the prior art, several methods are used to convert the interlaced image signals into progressive signals (de-interlace), as described below. Conventional technologies are described in detail with reference to FIGS. 2a to 2c showing conventional methods of generating fields using line interpolation.
FIG. 2a illustrates a line repetition method, which performs de-interlacing through a scheme of simply repeating the line information of a current field to implement one frame. Such a line repetition method can be implemented using simple hardware.
FIG. 2b illustrates an inter-field interpolation method without motion compensation, which implements a single frame by simply inserting the line of a previous field between the lines of a current field. Even an inter-field interpolation without motion compensation can be implemented using simple hardware.
FIG. 2c illustrates an intra-field interpolation method, which implements a new field by inserting data, obtained by dividing two line data by 2, between two lines so as to interpolate a region between two lines in one field. Such an intra-field interpolation method is advantageous in that it improves an image quality compared to the line repetition method, and decreases an error occurrence probability compared to the inter-field interpolation without motion compensation.
According to the conventional interpolation methods, the line repetition method is disadvantageous in that an image quality is deteriorated after interpolation. Further, the inter-field interpolation method without motion compensation is advantageous in that it can be implemented using simple hardware, but it is disadvantageous in that an error occurs or an image is degraded and then an image quality is deteriorated even though interpolation is performed with respect to moving images. Further, the intra-field interpolation method is advantageous in that it improves an image quality compared to the line repetition method and has an error occurrence probability lower than that of the inter-field interpolation method without motion compensation, but it is disadvantageous in that a still image is degraded after interpolation, thus deteriorating an image quality.